THE HAGUE, Netherlands (AP) — The Dutch government raised its terror threat level Wednesday from "limited" to "substantial," saying Dutch citizens are traveling to Syria to fight in the civil war and could return battle-hardened, traumatized and further radicalized.

"The chance of an attack in the Netherlands or against Dutch interests abroad has risen," the country's National Coordinator for Security and Counterterrorism said in a statement.

The warning comes just two months before hundreds of thousands of people are expected to descend on Amsterdam for mass celebrations around the abdication of Queen Beatrix and investiture of her son, Crown Prince Willem-Alexander, as the country's new king.

The government cited the threat posed by jihad fighters returning from Syria, where rebels are battling the government forces, and signs of increasing radicalization among Dutch youth at home as key reasons for lifting its threat level to substantial, the second-highest level on the four-step scale, just below "critical."

Counter-terror chief Dick Schoof said that nearly 100 people had travelled from the Netherlands to Africa and the Middle East, mainly to Syria to fight in conflicts there, and he warned it is not just a Dutch problem.

"From Europe as a whole, hundreds have made the journey, many of whom are joining local armed groups," the counter-terror watchdog said.

"These jihadist travelers can return to the Netherlands highly radicalized, traumatized and with a strong desire to commit violence, thus posing a significant threat to this country," Schoof said in his statement.

He said that several fighters have already returned to the Netherlands.

"They are known and they are being monitored," he told national broadcaster NOS.

Government terror experts also say that political upheavals in North Africa and the Mideast are giving terror networks room to grow.

Schoof said Dutch intelligence and law enforcement agencies are working with other European allies to contain the threat. More intelligence staff are monitoring "jihadist travelers" and police are stepping up efforts to tackle radicalization in Dutch towns and cities.

Last month, France also expressed concerns about its citizens heading to Mali to join radical Islamic fighters there, even as the French army was fighting the Muslim rebels in its former colony.

French police arrested four youths last month suspected of trying to join radical Islamic fighters in West Africa, and expelled radical imams and others considered risks to public order.

Police in the port city of Rotterdam arrested three men in November on suspicion of preparing to travel to Syria to fight alongside rebels.